Thermocapillary flow near a hemispherical bubble on a heated wall

Abstract

The flow driven by variations in surface tension round a hemispherical gas or vapour bubble on a heated wall has been investigated numerically for steady-state conditions over a wide range of values of dimensionless parameters, and experimentally for one set of conditions. Although six parameters are needed to specify the flow conditions, the magnitude of the liquid flow normal to the heated wall is determined primarily by tihe Marangoni number, Prandtl number and the Biot number based on the effective heat-transfer coefficient at the liquid-gas interface. The interior temperature of the bubble depends in addition on the thermal conductivity ratio of the liquid and the wall material. The flow is very sensitive t o the presence of surface-active contaminants. For water, calculations and experimental observations both indicate that contamination which lowers the static surface tension by only 0.1% may suppress the thermocapillary motion.

The Influence of the Magnitude of Gravitational Acceleration on Marangoni Convection About an Isolated Bubble under a Heated Wall

“…From experimental observations [2,6,7] it is known that the 255 flow field is symmetric about the bubble vertical axis. Furthermore, results by Kassemi and Rashidnia [4] show the onset of unsteady oscillatory and three-dimensional (3D) flow occurring at a critical Marangoni number of approximately 12,000.…”

“…When a small gas bubble is situated on a heated wall, the difference in temperature between the overheated base and the cooler tip of the bubble 30 causes the surface tension gradient [2]. The net surface tension force on any element of the interface is opposed by viscous shear stresses in both the gas and liquid phases [2], but since the shear stress in the liquid phase is typically much greater than that of the gas phase, the gas phase may be neglected, as has been the 35 case in previous numerical investigations [2,3]. Most natural convection processes on earth are buoyancy driven, caused by the density gradients within fluids resulting from temperature gradients within the system.…”

Thermocapillary Flow and Aggregation of Bubbles on a Solid Wall

“…[5], [6], and [19]-[21] for a given U r , integrate to find the drag force on the bubble, and then calculate q from Eq. [15] as a function of the gap between the bubble and the solid wall.…”

Temperature and velocity fields due to surface tension driven flow

“…Mechanism of thermocapillary convection in surroundings of a bubble under a heated horizontal wall (similar to Kao and Kenning 1972) diagonal corners. In the middle of this plate was a capillary opening with a connection to the syringe for the bubble injection.…”